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Ohm's LawEquipment1Modular CircuitsEM-3536-KIT1Modular Current SensorEM-35341Voltage SensorUI-510014mm Banana Plug Cords-Red Set of 5SE-9750Required but not included:1550 Universal InterfaceUI-50011PASCO CapstoneIntroductionThe purpose of this experiment is to verify Ohm’s Law for commercially manufactured resistors and to examine the limits of validity for Ohm’s Law. The behavior of resistors, a diode, and a light bulb are examined. TheoryIn metals and some other materials (in particular, commercially manufactured resistors), one finds experimentally that the voltage drop, V, across the material is directly proportional to the current, I, through the material (provided the temperature remains relatively constant):V I which is referred to as Ohm’s Law. It is convenient to define a proportionality constant called the resistance (unit: Ohm [Ω] = V/A) such that V = IR.(1)3511550806450 A resistor generally means a device that obeys Ohm’s Law (many devices do not) and has a resistance R. Figure 1: Circuit DiagramFigure 2: Ohm’s Law SetupSetupIf an ohmmeter is available, use it to check the resistance of the 100 Ω resistor. To connect the ohmmeter, insert a metal connector into each of the electrical clips on the resistor module and use alligator clips to attach the meter to the metal connectors. Note that you must check the resistance when the resistor is not connected to the rest of the circuit.Setup the circuit shown in Figure 2 using the 100 Ω resistor. Turn on the Wireless Current Module and connect it in the software.In PASCO Capstone, click open the Signal Generator at the left of the screen. Set the output to a Triangle Waveform with a Frequency of 0.1 Hz and an amplitude of 3.0 V. Click Auto. Click the Signal Generator again to close the panel.Set the sample rate for the Voltage Sensor to 40 Hz.Create a graph of Voltage vs. Current.ProcedureClick RECORD. Collect data for about 10 seconds (one full cycle) and then click STOP. The graph (Output Voltage vs Output Current) should show a straight line (with some noise.)Click on Data Summary at the left of the page. Double click on any Run #1 and re-label it “100 Run”. Click Data Summary again to close it. Replace the 100 Ω resistor with a 33 Ω (green-blue-brown-gold) resistor. As before, check it with an ohmmeter if one is available.Click RECORD. Collect data for about 10 seconds and then click STOP. Re-label this run “33 Run”Replace the 33 Ω resistor with the light bulb module.Click RECORD. Collect data for about 10 seconds and then click STOP. There should be a funny kink in the graph. Observe what the bulb is doing as the kink occurs. Answer Question 5 in Conclusions. Re-label this run as “Light Bulb”.37594862450942043356261100Replace the light bulb module with the spring clip module and place a diode in the spring clips as in Figure 3. Note that the diode looks like a small black resistor with one grey end. Arrange the diode so the grey end is “up” toward the red lead from the 550 Interface. Figure 3: Diode “up” SetupFigure 4: Diode “up” Circuit DiagramClick RECORD. Collect data for about 10 seconds and then click STOP. Re-label this run as “diode up”.Reverse the diode so the grey end is “down” toward the black lead.Click RECORD. Collect data for about 10 seconds and then click STOP. Re-label this run as “diode down”.Analysis: Ohm’s Law for a ResistorClick once on the multicolored Run Select icon in the graph toolbar to show more than one data set. Then click on the black triangle by the Run Select icon and select the “100 Run” and the “33 Run”. Both should show on the graph.Click on the Scale-to-Fit icon on the graph toolbar.Select the “100 Run” data by clicking on it in the legend box or by clicking the “100 Run” data on the graph.Click on the black triangle by the Curve Fit icon on the graph toolbar and select Linear.Repeat for the “33 Run” data. You may need to drag one of the Linear boxes to see both of them at the same time.Answer Questions 1-4 in the Conclusions section.Analysis: Light BulbClick on the black triangle by the Run Select icon and select the “Light Bulb” run.Click on the Scale-to-Fit icon.Answer Question 6-8 in the Conclusions section.To help answer Question 8, hook up the lamp again as in Figure 2. Click open Signal Generator and set output 1 for a Frequency of 0.01 Hz and an Amplitude of 3.0 V. Click Auto. Click RECORD and let it run for one full cycle (100 s). You should see both this run and the “Light Bulb” run on the graph. If not, use the Run Select icon to select both. Is the answer to Question 8 more clear now? Re-label this run “lamp slow”. Wait a minute! Tungsten is a metal and the metals are supposed to obey Ohm’s Law. What is going on? Turn off “Light Bulb” so only “lamp slow” is displayed on the graph. Click on the Selection icon and drag the Selection box handles to select the data where voltage is between -0.1 V and +0.1 V and current is between -0.05 A and +0.05 A. Click the Scale-to-Fit icon. Click on the black triangle by the Curve Fit icon and select Linear. Answer Question 9 in the Conclusions section.Analysis: DiodeClick on the black triangle by the Run Select icon and select the “diode up”, and “diode down” runs. Both curves should show at the same time.Click the black triangle by the Run Selection icon and select “100 Run” in addition to the “diode up”, and “diode down” runs. Note that all three curves have the same x-intercept (where V = 0). The current is zero here, but probably does not read zero due to the zero error in the current sensor. Assume the current is actually zero at this point and answer Questions 10-12 in the conclusions.Ohm’s Law ConclusionsWhy do the lines formed by the data have some width?Why do the “100 Run” line and the “44 Run” line cross on the V = 0 axis?How well do the resistors obey Ohm’s Law? Explain fully how you know!What is the physical meaning of the slope of the Linear Fit to the data on the Ohm’s Law graph? Hint: What are the units of the slope?What is the bulb doing during the kink in the curve?What evidence is there that the light bulb does not obey Ohm’s Law?Why doesn’t the light bulb obey Ohm’s Law?Why are there two curves? That is, why are there two values of current for each voltage near the kink? And why is there a kink?Is there any region where the light bulb obeys Ohm’s Law? Why?Does the diode obey Ohm’s Law? How do you know?Does the diode conduct in both directions? Explain fully.When does the diode conduct? ................
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